The fabrication of an organic/inorganic thin film is a fundamental technology in nanotechnology. It is a technology essential for most electronic devices such as mobile phones, military equipment, solar cells, etc., which need to be lightweight, thin and bendable.
Vacuum deposition has been the representative technology for formation of an organic/inorganic thin film since the mid-20th century. There has been a lot of advancement focused on electronic materials and many methods have been proposed. The vacuum deposition techniques include physical deposition and chemical deposition methods. And the wet deposition techniques include electro-plating, spin coating, slot-die coating, etc.
High-performance electronic devices using organic/inorganic thin films are being researched actively around the world. Also, in the industry, investments are being made consistently in the development of new technology for productivity improvement and cost reduction because the organic/inorganic thin film formation is a fundamental technology in electronic devices such as semiconductors, displays and solar cells. In the light of this global trend, it is expected that the investment will be expanded further and competitions for breakthrough thin film formation technologies that can produce thinner and cost-effective devices will become more increasingly fierce.
Organic solar cells can be given as an example of the reason why a new technology for forming organic thin films is necessary. The organic solar is drawing attentions as a next-generation solar cell because it can be produced at low cost and is light and flexible. With low price and light weight, it is applicable to most fields where energy harvesting is necessary, such as batteries for mobile phones, military equipment, etc.
Despite the high marketability and applicability, there is an obstacle to the commercialization of the organic solar cell considered as the next-generation energy source due to the difficulties in large-scale process and the R2R (roll-to-roll) process. Although many researches are being conducted on processes for large-scale process, it is difficult to fabricate large area organic solar cells with high efficiency due to the difficulty in the control of nanomorphology over a large area.
Although the spin coating method has been considered the most effective method for fabricating high-efficiency organic solar cells capable of controlling nanomorphology, it is disadvantageous in that it is inappropriate for commercialization because it is impossible to achieve large-area thin film. Although large-area thin film can be achieved with many thin film forming methods such as doctor blading, slot-die coating, etc., it is difficult to fabricate high-efficiency organic solar cells due to the difficulty in forming uniform thin films because they are very sensitive to such factors as ink composition, interaction between the ink and the surface, etc.
Reference can be made to Korean Patent Registration No. 10-1189172, which was granted on Oct. 2, 2012 and issued on Oct. 10, 2012, for a method for fabricating a large-area organic solar cell. Although the patent describes that a thin film for a large-area organic solar cell with a flat surface can be prepared by using a spray coating apparatus wherein a feed solution is injected into a center portion and a high-pressure gas is injected around the center portion, it does not solve the problem of significant material loss during the thin film formation through spin coating or remarkably improve the uniformity of the thin film.
(Patent Document 1) KR 10-1189172 B